Age affected: Growers/finishers (all ages).
Causes: Mycotoxins; trauma; constipation; dietary problems; tethered on steep slope.
Effects: Red lining of rectum protrudes from anus.
Rectal prolapse may occur in pigs or any age but is more common in males aged 14-16 weeks. There are a number of predisposing factors. A genetic predisposition has been identified. In male piglets it may follow straining resulting from the impaction of phosphate crystals in the urethra. The condition has been reported to follow the inclusion of 20% excess lysine in the diet.
In weaned pigs it may follow diarrhoea although severe straining is necessary before this occurs. Medication with tylosin and to a lesser extent other antimicrobials may trigger prolapse which is accompanied by soft faeces and by coughing. The raised abdominal pressure of alarm calls during fighting causes the rectal mucosa to protrude visibly and it can be damaged when pigs are mixed and fight.
The hyperoestrogenism associated with zearalenone may predispose to the condition in sows but rectal prolapse in the sow usually follows farrowing or tethering or housing heavily gravid sows with the hindquarters lower than the body or hanging over a drop. The prolapsed rectum may become reduced naturally, become strangulated, necrotic and drop off or be bitten off by the other pigs. Rectal stricture, death from loss of blood or peritonitis may all occur.
Mode of transmission
There is no single cause of rectal prolapse, and the condition cannot be transmitted directly to another farm unless the conditions are replicated. When the predisposing factors include disease such as salmonellosis or some pneumonias, then the transmission of the agents responsible may predispose to the condition, but it does not follow that rectal prolapse will occur in every batch of infected pigs.
Rectal prolapse may be seen as a large reddish cylinder of the rectal mucosa protruding from the anus of the affected pig. It may be small (less than 2-10 cm in length) or large and oedematous. Rectal prolapses are rapidly damaged by the animal as it backs into structures such as pen walls or by other pigs in the pen which bite it. It many cases, the first evidence that rectal prolapse has occurred in a group is the presence of blood on the mouths of a number of animals in the pen.
Lacerated or necrotic (dead and blackened) prolapses may also be found. Pigs may be found dead without the prolapse having been seen or, in some cases, the prolapse drops off before being noted. Where pigs are affected by zearalenone, there is usually vulval enlargement in females and some enlargement of the udder. Where diarrhoea is associated with the cause, diarrhoea is present in other animals in the group.
Attention may be drawn to an affected pig as a result of biting or the prolapse may be seen. Early or transient prolapses may be visible as brief flashes of pink or red mucosa which are withdrawn after straining or defecation stops. The cause may be identified both in life or at post-mortem if diarrhoea and straining are the cause, or if hyperoestrogenism is involved.
When pigs have died from rectal prolapses, the prolapse is generally visible and diagnosis is straightforward. If the animal is decayed however, the rectal mucosa balloons outward and this ballooning may be mistaken for prolapse. When the prolapse has dropped off or been chewed off in life or after death, examination of the rectum reveals the severed end or the ring of scarring left. When this has progressed to rectal stricture, the fact that rectal prolapse was the original cause of the stricture can only be determined from the clinical history.
Treatment and prevention
Animals must be separated from their fellows to avoid being killed. Small or transient prolapses may resolve spontaneously. In most cases, the prolapse must be reduced surgically (pushed back into the body) under local anaesthetic and secured by a purse-string suture. Where serious damage has occurred or where the prolapse cannot be reduced manually, it must be amputated surgically under local anaesthetic after the portion to be retained has been sutured in place.
Animals may be treated in their groups by the insertion of an 18-20 cm helical corrugated plastic tube of 1.5 cm in diameter for weaners and fatteners and 2.0 -3.0 cm diameter for sows into the prolapse. Heavy duty rubber bands are placed over the prolapse near the anal ring. Tube and prolapse drop off after 5-7 days. Affected animals of slaughter weight may be penned separately and transported for slaughter, but extensively and irreparably-damaged animals should be slaughtered humanely.